A conventionally known example of a displaying technique that allows the inside of a lumen to be observed is a fly-through view with virtual endoscopic (VE) images. Such a fly-through view uses three-dimensional medical image data (volume data) including a luminal tissue. A VE image is an image that is generated from volume data using a perspective projection from a viewpoint position and a line of sight set inside of a lumen. A fly-through view is a technique for displaying VE images at different view positions as dynamic images, by shifting the viewpoint position along the center line (central line) of the lumen. Fly-through views are mainly used for volume data including digestive organs such as a large intestine acquired using an X-ray computed tomography (CT) apparatus or a magnetic resonance imaging (MRI) apparatus.
Recently having been put in practical use is an ultrasonic diagnostic apparatus that generates volume data along a time sequence approximately in real time, using an ultrasonic probe that can perform three-dimensional ultrasonic scanning. In the field of ultrasonic examinations as well, fly-through views using B-mode volume data including luminal tissues have come to become implemented increasingly. However, because of the nature of an ultrasonic diagnostic apparatus, an ultrasonic diagnostic apparatus is not suitable for observations of organs such as digestive organs not filled with water or substance. Hence, fly-through views using an ultrasonic diagnostic apparatus have been applicable to a lumen filled with fluid, e.g., a blood vessel filled with blood, or a bile duct filled with bile.
An ultrasonic diagnostic apparatus is a medical image diagnostic apparatus having a higher representation resolution for microstructures, compared with other medical image diagnostic apparatuses such as an X-ray CT apparatus and an MRI apparatus, and is useful for observing the circulatory system, mainly blood vessels. For example, a fly-through view of a blood vessel using an ultrasonic diagnostic apparatus is useful as a new approach for observing a circulatory disease such as hemadostenosis or an aneurysm. When a fly-through view of a lumen is to be provided, the inner wall of the lumen will be the clipping region, which will be the target of rendering.
However, contours between structures tend to blur more in an ultrasonic image (B-mode image) than in other types of medical image such as an X-ray CT image or an MRI image. Therefore, it has been difficult to use a computer program to automatically detect the inner cavity region of a lumen in B-mode volume data, unless the lumen has a certain diameter or larger. Therefore, a fly-through view in an ultrasonic diagnostic apparatus is currently limited to a tubular tissue having a certain diameter or larger, and it has been difficult to apply a fly-through view to thin tubular structures.